Method of and apparatus for burning coal



April 26, 1949. D. E. sTAlR 2.468.415

METHOD OF AND APPARATUS FOR BURNING COAL Filed Aug. 17, 1945 5Sheets-Sheet 1 INVENTOR.

April 26, 1949. D E sTAlR 2,468,415

METHOD OF AND APPARATUS FOR BURNING COAL Filed Aug. 17, 1945 5Sheets-Sheet 2 IN V EN TOR.

BMM/MMV April 26, 1949. D. E. sTAlR 2,468,415

METHOD oF AND APPARATUS FOR BURNING coAL Filed Aug. 17, 1945 5Sheets-Sheet 3 1N V EN TOR.

April 26, 1949. D. E. sTAlR METHOD OF AND APPARATUS FOR BURNING COAL 5Sheets-Sheet 4 Filed Aug. 17, 1945 INVENTOR. BYQM f f/wy 1n.

5 Sheets-Sheet 5 D. E. STAIR METHOD OF AND APPARATUS FOR BURNING COALApril 26, 1949.

Filed Aug. 17, 1945 V IN V EN TOR. @WMM 6 M' A ffy;

atentec pr. 26, 1949 UNITED STATES PATENT oFPIcE METHOD oF AND APPARATUSFou BURNING CoAL Daniel E. Stair, Chicago, Ill.

Application August 17, 1945, Serial No. 610.991

- Claims. l

This invention relates to an improved method of burning coal and tocertain new and useful improvements in apparatus for carrying out theseveral steps of the improved method.

A principal object of the invention is to provide an improved andpractical method of burning coal, whereby coal of various qualities maybe converted and 'burned either individually or as mixed'fuel in thesame apparatus.

Another principal object is to provide a method for burning coal whichinvolves complete 'conversion of the volatiles and the fixed carbonsinto heat energy before delivering the hot combustion products into theheat transfer chamber of the heating apparatus, whereby the maximum heatunits are utilized in connection with the heating operation.

The various methods of burning coal in fuel beds, as heretoforepracticed, have included introducing the coal directly into the heattransfer chamber, to-wit, the usual re box of a furnace, which is inclose association with the boiler.' Consequently, the temperature of thefire bed is so reduced by the transfer of heat to the boiler or to thewater coils thereof, that insuiiicient heat is retained in the fire bedto break down the cellular structure of bone coal surrounding particlesof fixed carbon and thereby liberate this carbon in the form of heatunits.

It is a specific object of the present invention to provide an improvedmethod for burning coal in a fire bed in which the coal is advanced inan angular course through zones of progressively increasingtemperatures, which temperatures insure complete' liberation of allcombustible substances contained in the coal, and whereby the angularconiiguration of the iire bed will permit diierent amounts of air topass through different zones of the re bed and thereby insure completeand efficient combustion of the free and the fixed carbons of the coal.For example, the configuration of the coal bed is such that there isless resistance to the air currents passing through the cooler upperportion of the bed in which a major portion of the more volatilecombustibles are liberated or to which they migrate from other zones. Inthis way, the volatile gases are supplied with the proper amounts ofcombustion air and the air iiow through the lower and higher temperaturezones of the bed may be restricted so as to avoid cooling theincandescent fuel.

A further object of the invention is to provide a combustion chamber inwhich the zone of highest temperature will be near the bottom of thechamber and thereby expedite the removal of the ash and othernoncombustlble portions of the fuel from the fuel bed in the form ofliquid slag.` In this way, the invention avoids the collection of flyash in the :dues of the boiler and also avoids the matting together ofthe incandescent fuel particles in the combustion chamber or theformation of clinkers therein in a manner to obstruct the passage ofair'.

Another object is to provide an improved method4 of burning coal inwhich the temperature changes in the heat transfer chamber of theheating apparatus will be gradual and consequently avoid the recurrentabrupt expansion and contraction of the boiler and other metal parts ofthe furnace.

Another object is to provide an improved apparatus having a preferredform of combustionl chamber adapted for use in connection with thevarious furnace constructions now in general use and which isparticularly adapted for use in connection with the simplified meansherein shown for automatically advancing the coal through the combustionchamber.

A further object of the invention is to provide a fuel advancingmechanism in the form of a revolvable retort which will move the coalthrough the combustion chamber and at the same time agitate the coalwithin the retort, by moving it from the lower portion to the upperportion thereof and thereby keep it relatively loose so that thecombustion supporting air may pass freely through the upper portions ofthe coal bed to combine with the free carbons liberated from the coal.

Another object of the invention is to provide improved structure forforming adequate `air passages leading into the lower portion ofthe coalbed within the combustion chamber and to provide controllable means forvarying the amount of air entering the combustion chamber in proportionto the heating requirements of the furnace. In this connection, theinvention includes the provision of a suction fan and dampers interposedbetween the fan and the combustion chamber, the dampers being controlledto vary their positions relative to the temperature or pressure of theboiler so that the air drawn into the combustion chamber will beproportional to the furnace temperatures or the boiler pressure.

Another object of the invention is to provide a convenient means forremoving the revolvable retort when it is necessary to repair any partof the combustion chamber, `whereby these repairs can be taken care ofwith minimum delay and inconvenience.

, 3 Another object is to provide a simplied means i'or removing anddisposing of the slag discharged from the combustion chamber. In thisconnection, the invention includes the provision of a pit and acontainer removably positioned therein to receive waste water; themolten slag being discharged from the combustion chamber directly intothe water filled container.

The improved method of the present invention and a preferred form ofapparatus for carrying out the steps of the method are illustrated inthe accompanying drawings wherein:

Fig. l is a front view of a revolvable retort, and the mechanismsassociated therewith.

Fig. 2 is a side view of the structure shown ln Fig. 1 showing parts ofthe furnace broken away to illustrate the path of travel of thecombustion gases.

Fig. 3 is a vertical section taken substantially online 3-3 of Fig. 1but illustrating only a portion of the boiler and heat transfer chamberof the furnace.

Fig. 4 is a fragmentary sectional view taken substantially on li'ne 4 4of Fig. 3, looking in the direction indicated by the arrows.

Fig. 5 is a similar fragmentary sectional view which is takensubstantially on line v5---5 of Fig. 3.

Fig. 6 is an enlarged fragmentary sectional view illustrating an I-beamgrate construction which provides a series of tuyre passages leadinginto the lower portion of the combustion chamber.

Fig. 7 is a faceview of a base ring which encloses a gear for rotatingthe revolvable retort.

Fig. 8 is a fragmentary plan view of certain of the operating elementswhich are shown removed from their operative positions on the base ringfor the purpose of clearness.

Fig. 9 is a fragmentary sectional view taken through the base structuresubstantially on line 9-9 of Fig. 1.

Fig. 10 is a detail view of side frame members for slidably supportingthe retort structure in its operative position. l

Fig. 11 is a partial sectional View to further illustrate the supportingframe structure of Fig. 10, the said sectional view being taken on linelI-H OfFig. 2.

According to the improved method which forms a. part of the presentinvention, the coal bed is so maintained as to provide a generaltriangular configuration in vertical section so as to progressivelydecrease the mass of material toward the upper limit of the bed andthereby permit combustion air to pass more freely through the upperportions of the bed than through the lower portions thereof. In order tomaintain a coal bed of the desired configuration, a combustion chamber IIl is provided which includes a relatively large bowl portion I l forreceiving the fuel and an outlet passage I2 connected therewith. Thesaid A bowl portion I I and the outlet passage extend at angles to eachother so that the longitudinal axis of the bowl portion extends upwardlyand out'- wardly from the furnace and the longitudinal axis of thedischarge passage extends upwardly and inwardly. This passagecommunicates with lthe heat transfer chamber I3 of the furnace.

The coal is passed through a retort so as to subject it to heat andthereby release large amountsl outwardly inclined axis so as to keep thecoal in agitation by continuously moving it from the lower portion ofthe retort into the upper portion thereof. This agitation of the coalkeeps it loose so as to permit the air to flow through the upper strataof the fuel bed with less obstructionthan through the lower portion, buthigher temperature zones of the bed. According to the improved method,the fuel bed is maintained at a sumcient depth and the air is passedlengthwise through the bed, with increasing resistance toward the lowerportions thereof so that the temperature of the fuel bed progressivelyincreases from the top to the bottom thereof, the zone of highesttemperature being at the lower portion of the combustion chamber. Inthis way, the several stages of combustion will be carried outsimultaneously. For example, the high volatile free carbons contained inthe coal are distilled off in the cooler upper Strata of the fuel bed,particularly that p0rtion of the bed which is contained in the retortand in the cooler portion of the combustion chamber adjacent to theretort. Certain other of the free carbons are liberated from the coal inthe lowery zone of higher temperature and migrate upwardly through thefuel bed toward the upper strata thereof wherein they are mixed with thecombustion air passing through this strata of the coal bed. The fixedcarbons of the coal which require higher temperatures to convert theminto combustible gases are liberated from the fuel in the lower andconsequently. higher temperature zones of the fuel bed. 'I'he finalstage of combustion takes place in the lowest strata of the fuel bedwhich is maintained at a sufficiently high temperature to break down thebone coal cellular structure so as to free the combustible carbonsentrapped therein and to liquefy the ash and other noncombustiblesubstances contained in the coal so that these materials are removedfrom the re bed in the form of a molten slag.

The.air is preferably drawn through the fuel bed by a controlled suctiondevice as distinguished from an ordinary stack and the operation of thisdevice together with dampers associated therewith are controlled bytemperature responsive means associated with the furnace. In this way,the volume of air drawn through the re bed will be controlled inrelation to the temperature desired to be maintained. The combustiblegases distilled from the coal and migrating toward the upper portion ofthe fuel bed are carried by the air currents into the higher temperaturezones where they are burned.V For example, a portion of the gasied fuelmay be carried downwardly and directed into the heat transfer chamberthrough the discharge passage I2 as shown by the path of arrows in Fig.3. Another portion of the said gases may be directed into the heattransfer chamber through a plurality of ducts I4 which pass through thewall of the furnace immediately above the arch I5 of the dischargepassage l2. Inasmuch as the lower portion of the fuel bed providesgreater resistance to the passage of air, my improved method includesthe introduction of air through tuyre passages which extend into thefuel bed at a location intermediate the top and bottom thereof andthrough passages at other locations near the bottom of the fuel bed;These passages are provided with damper doors which function inconnection with flue dampers to control the volume of air passing intothe combustion chamber. Preferably, the same device which is utilized tocontrol the position of the ue dampers controls the position of the saiddamper doors.

In addition to agitating the coal contained in the retort, the coal isadvanced through the combustion chamber in a downwardly and thenupwardly directed path so that each particle of coal will pass throughthe several temperature zones of the combustion chamber and thereby becompletely converted into combustible gases and the hot products of thiscombustion are directed into the heat transfer chamber of the heatingapparatus. Inasmuch as the complete conversion of the coal takes placeoutside of the heat transfer chamber, the absorption of heat by theboiler or by water coils arranged in the furnace does not materiallyaffect the temperature of the fuel bed and therefore makes'itpractlcable to maintain the high temperatures re- 'quired to liberateall combustible products of Fig. 3, unite with a curved bottom portionas shown in Fig. of the drawings. The side wall A of the bowl Ilterminates at the entrance end of the discharge passage I2 and divergesfrom the plane of the mouth of the bowl I I so that the combustionchamber will have a general triangular configuration in vertical sectionas shown in Fig. 3 of the drawings, and the wall A will dene the generalslope of the inner inclined face of the fuel bed.

The combustion chamber is separated from the heat transfer chamber I3 ofthe furnace by means of a wall of refractory material which defines thedischarge passage I2. This manner of construction removes the fuel bedfrom the cooling influence of the boilers I6 and other heat absorbingelements located in the transfer chamber and also makes it practicableto make the walls defining the said chamber II and passage I2 as thickas maybe necessary to provide the desired heat insulation to maintainrelatively high temperatures within the combustion chamber. Inconnection with the combustion chamber as herein illustrated, thepresent disclosure includes a tubular boiler I6 arranged horizontallyabove the heat transfer chamber I3 so that the hot combustion productswill flow through the boiler ilues. It will be understood however thatthe speciiic form of boiler and heat transfer chamber is not important,but is shown herein merely for convenience of illustration. Thecombustion chamber and other parts associated therewith for advancingthe fuel through the combustion chamber may be used in connection withfurnace structures and boilers of various types.

The lower portion of the combustion chamber I0 is provided with airinlet openings I1, I1 for the admission of air; the amount of air beingcontrolled by means of dampers I8, I8 in connection with other dampermeans hereinafter described. A series of I-beams I9 are arranged inclose relation to each other to provide a grate structure extendingaround a portion of the combustion chamber. The top webs of the I-beamsare, preferably, of less width than the bottom webs 2l so as to permitthe said I-beams to be arranged in a radial pattern as shown in Figs. 4

and 6 of the drawings. The spaces between the said I-beams provide tuyrepassages 22 through which air is directed into the lower portion of the'combustion chamber II) so that an adequate supply of air will passthrough the body ofv material lying in the lower and higher temperaturezones of the combustion chamber I0. The coal -is constantly fed into theretort so as to keep a desired level of coal therein. By reason of theconfiguration of the combustion chamber and the inclined arrangement ofthe revolvable retort, the normal upper and lower capacity lines of thefuel bed are inclined relative to each other as indicated by thereference numerals 23 and 24 respectively in Fig. 3 of the drawings. Theside of the fuel bed represented by the numeral 24 extends across thedischarge passage I2 while the other inclined side of the fuel bedextends diagonally across the retort chamber.

The retort is of circular structure and is com-A posed preferably of aplurality of segments 25. The segments are made of cast metal and haveinwardly extending flanges 26 at their opposite edges which are securedto corresponding flanges of an adjacent segment to provide inwardlyextending vanes 21. The outer ends of the retort segments 25 are securedtogether by means of a flanged ring 28, one flange of which overlaps theouter ends of the segments and another flange 29 thereof extendsinwardly for a short distance along the inner edges of the vanes 21.Preferably, the seams between adjacent segments 25 of the retort andbetween the outer ends of the segments and the flange ring 28 are sealedto provide air tight constructions. The upper portions of the retort,therefore, serve as a trap for retaining any of the distilled freecarbons which may rise upwardly through the coal bed and enter the upperportion of the retort. The combustible gases thus entrapped will beentrained with the air currents passing into and through 'the retort andcarried into the high temperature zone for combustion. The lower portionof the retort is tapered to provide a cone configuration and the outersurface of this portion is provided with a ring gear 30. The gear 30 maybe secured to the retort by any suitable means, for example, by bolts 3|which extend through the ring gear and into a shoulder portion 32 formedon the retort segments. The teeth 3| of the ring gear are formed on theouter periphery thereof and are of awidth less than the thickness of thering.

The lower face 32 of the ring gear and the smooth peripheral portion 33thereof, adjacent the teeth 3I provide bearing spaces which engagecorresponding surfaces of a base ring 34 which seats upon the upper faceof a base casting 35.

The base casting 35 is of rectangular construction, but is provided witha circular opening which receives an inwardly extending rib 36 formed onthe bottom surface of the base ring adjacent its inner perimeter. 'Ihecentral opening through said base casting 35 together with the inclinedouter wall of the retort define an air space 31 which extends entirelyaround the retort and communicates with the bowl portion I I ofv thecombustion chamber. At the lower portion of the said bowl Il, the saidair is delivered into the combustion chamber through the spaceintervening between the grates and the outer surface of the retort andthrough the tuyre passages 22 between the grate members. 'Ihe lowerportion of the base casting 35 is provided closing of this inlet openingis controlled by a damper door 39 which is automatically opened andclosed simultaneously with the openingand closing -of damper doors I8,I8.

The retort is rotated preferably at a low'rate of speed by means of anelectric motor 40 which may be supported on a shelf 4I secured to thebase ring 34. 'I'he motor shaft is provided with a. worm (not shown)which meshes with a worm gear 42 enclosed within a housing 43 (Figs. 1and 8) The worm gear 42 is connected by means of a shaft 44 with apinion 45 which meshes with the teeth 3| of the ring gear 30.

It will be seen from the above description .that

Y the operation of motor 40 will rotate the retort about its axis whichinclines at a suitable angle to maintain the capacity line 23 of thefuefwithin the retort substantially at the inclination shown in Fig. 3of the drawings. The lower ends of the retort segments are provided withimpeller elements 46 which are -in the form of Z-bars curved to conformto the circular structure of the retort segments and having their loweroutturned flanges 41 inclined in the direction of their length and inthe direction of rotation of the retort so as to exert wedging pressureon the body of fuel within the bowl portion II of the combustionchamber. During this rotation` of the hopper, the inwardly projectingvanes 21 bustion air into the combustion chamber, for example' whenincreasing the re after'a prolonged inactive period. a damper 61positioned in a branch draft passage 68 leading to the chimney 52 may beadjusted to any desired position. However, during normal operation ofthe l furnace, the damper 61 is closed. After the temperature of thefurnace approaches its maximum, the operation of the pressure motor 54will function to'proportionately adjust the positionsand other metalparts of the furnace.

thereof keep the coal in constant agitation by moving the coal from thelower portion of the retort and discharging it onto the upper portion ofthe coal bed. The supply of coal to the retort may be maintained by any.suitable means, for example, a spout 48 which may lead from a source ofcoal supply (not shown) Draft Control The amount of combustion air drawninto the combustion chamber is controlled, preferably, by inductionmeans, for example a suction fan 49, which is preferably operated at acontinuous speed by means of a suitable motor 50.

from the discharge end of the boiler I 6 to the chimney 52. The degreeof suction for drawing air into the combustion chamber and for inducingthe flow of the products of combustion through the boiler tubes iscontrolled by the position of a damper 53 positioned in the draftpassage 5I.

-The position of the damper 53 and likewise the positions of the damperdoors I8, I8 and 39 are controlled by means of a pressure motor 54 whichresponds to temperature changes within the furnace.v The pressureactuated motor 54 is of conventional construction and includes an arm55, the inner end of which is pivoted at 56 to the motor. casing 54 andis operated by a pressure actuated rod 51. The outer end of the lever isconnected to the damper 53 by means of a cable 58 which extends'overpulleys 59 and 60, the latter of which is connected to the damper 53.The free end of the cable 58 is provided with counter weights 6I so asto maintain the cable taut at' all times. The damper doors I8, I8 and 39are connected to the arm 55 of the pressure motor 54 by means ofcooperating conecting rods 62, 63 and 64, the latter of which connectswith i thebell crank 65. Similar connecting rods for operating thedamper doors are arranged at opposite sides of the furnace and may beoperatively connected together by any suitable means, for example, shaft86 which connects the pulleys 59 located on opposite sides of thefurnace. When it is desired to manually increase the flow of com- Thefan is interposed in the draft passage 5I leading When it is desired tobank the re, the cable 58 and rods- 62 may be disconnected from themotor arm 39 so that the damper 53 and the damper doors I8 and 39 maybeclosed. The manually controlled damper 51 may then be opened slightly soas to permit a small amount of combustion air to be drawn through-thefuel bed by the natural or chimney draft.

Slag disposal As previously indicated in connection with the disclosureof the improved method, the ash and other noncombustible substancescontained inthe fuel are removed in the form of liquid slag. Thisslag-is discharged from the bottom of the combustion chamber through aduct 58 into a cinder disposal pit 10 located below the floor level ofthe furnace room. A removable container 1I in the `form of a bucket ispositioned in the pit 19 below the slag discharge duct 69, preferably apipe 12 discharges Waste water into the container 'II so that the slag,when discharged from the combustion chamber, will fall directly into abody of water and thereby instantaneously be cooled. This cooling actionon the slag, as it is discharged from the combustion chamber, forms itinto small particles. When the container 1I is filled with waste water,it will overow into the pit 10 until the water reaches the level to bedischarged through an overflow passage 13. When it is desired to emptythe container 1I, a drain plug 14 is removed so as to drain the waterfrom the pit 10. The bail 141iL of the container is then connected to asuitable hoist 15 to lift the container out of the pit as indicated indot and dash-lines in Fig. 3. Thev hoist 15 is movably supported on theover-head frame structure by means of a carriage 16. The carriageoperates on the outer flanges of I-beams 11, 18 of which the over-headframe is formed, Y

Removal of fuel hopper In order to facilitate repairing the grates orthe masonry of the combustion chamber, the retort is slidably supportedon a carriage 19 which is movably supported on the inner anges of saidI-beams 11, 18. The carriage 19 is provided with depending frame members89 and BI, the latter of which is inclined at an angle corresponding tothe inclination of the axis of the hopper and slidably supports channels82, 83 which are secured to diametrically opposite sides of the basering A$4. Cables 8l and 85 connect the channels `B2,

with a windlass 86 mounted in the framework of the carriage 19. Byrotating the windlass 88; the fuel hopper together with the base ring 34maybe drawn upwardly and outwardly until the impellers 46 at the lowerend of the hopper clear the base casting 35. The carriage 19 may then bemoved lengthwise of the I-beams 11, 18 to any suitable position whichwill provide free access to the combustion chamber for purpose ofrepair.

I claim:

l. The method of burning coal which consists in forming a fire bed ofsubstantially triangular` configuration in vertical longitudinalsection'so that the volume of coal therein progressively increasestoward the bottom of the bed, drawing' a stream of air through the upperportion of the opening of the combustion chamber to receive heattherefrom and deliver the coal into said bed from one inclined face tothe other, igniting and burning the fuel in the lower portion of the bedand along said opposite inclined face, feeding coal to the inclined faceof the bed at the air receiving side thereof and forcing it toward theburning inclined face of the bed, drawing air into the lower portion ofthe bed intermediate the inclined faces thereof, and agitating the coaladjacent said feeding side of the bed by moving the coal from a lower toan upper portion of the bed. V

2. A coal burning apparatus comprising means dening a heat distributingchamber, means dening a combustion chamber of angular configuration invertical longitudinal section separate from the heat distributingchamber butv communicating therewith, means including a revolvableretort for delivering coal into'the combustion chamber to maintain itfilled so as to form a fuel bed therein conforming to the shape of thecombustion chamber and for agitating the coal adjacent the receiving endof the combustion chamber, impeller means carried on the retort forforcing the fuel through the combustion chamber, and means for passing'air lengthwise through the fuel bed to mix with the combustion gasesliberated from the burning coal.

3. A coal burning apparatus including means dening a combustion chamberhaving a receiving opening for coal, a retort revolvably supported inthe said coalreceiving opening of the combustion chamber and revolvableabout an axis which inclines upwardly and outwardly from the combustionchamber and adapted to receive coal and deliver it into the combustionchamber, and impeller means carried by the retort for advancing the coalthroughthe combustion chamber.

4. A coal burning apparatus including means defining a combustionchamber having a receiving opening for coal, a retort supported toextend into the said coal receiving opening of the combustion chamberand revolvable about an axis which inclines upwardly and outwardly fromthe combustion chamber and adapted to receive coal and deliver it intothe combustion chamber, and impeller means comprising a series of wedgeshaped members carried by the retort for advancing the coal through thecombustion chamber.

5. A coal burning -apparatus including means dening a combustion chamberhaving a receiv ing opening for coal, a retort supported to extend intothe coal receiving opening of the combustion chamber and revolvableabout an axis which inclines upwardly and outwardly from the combus tionchamber and adapted to receive coal and deliver it into the combustionchamber,`impeller means comprising a series of wedge shaped mem-y lsocombustion chamber, means for rotating the retort, and inwardlyextending vanes fixed to the retort and movable therewith for agitatingthe coal contained therein during the rotation of Vthe retort, and aflange projecting inwardly from the side wall of the retort to partiallyclose the open end thereof and form a gas retaining trap.

A'1. In a coal burning apparatus including means defining a combustionchamber having a receiving opening for coal, a retort for receiving coaland for delivering it into the combustion chamber and comprising aplurality of segments secured together and supported to extend into thecoal receiving opening of the combustion chamber and revolvable about aninclined axis, means for rotating the retort, means at the junction ofsaid segments deiining inwardly extending vanes movable with the retortfor agitating the coal during the rotation of the retort, and a circularflange projecting inwardly from the side wall of the retort to partiallyclose the open end thereof and form a gas retaining trap.

8. A coal burning apparatus including means providing a heat transferchamber, means denning a separate combustion chamber formed with a coalreceiving bowl having an upwardly and outwardly inclined axis and anupwardly and inwardly inclined passage leading from said bowl into saidheat transfer chamber, there being a plurality of ducts connecting theupper portion of said combustion chamber with said heat transferchamber, a retort for heating the coal before it enters the combustionchamber, a base ring for supporting said retort with the lower end ofthe retort extending into the coal receiving opening of the combustionchamber, the said base ring also defining an air passage for supplyingair to the combustion chamber throughout the entire circumference of thecoal receiving opening of the combustion chamber.

9. A coal burning apparatus including means providing a heat transferchamber, a separate combustion chamber in the form of a bowl having anupwardly and outwardly inclined axis and an upwardly and inwardlyinclined passage leading from the bowl into said heat transfer chamber,there being a plurality of ducts connecting the upper portion of saidcombustion chamber with said heat transfer chamber, a retort supportedtc extend into said bowl of the combustion chamber and adapted toreceive coal and deliver it into the combustion chamber, means definingan air passage communicating with the entire circumference of the coalinlet opening of the combustion chamber for supplying air to thecombustion chamber at the lower end portion o! the retort, suction meansfor drawing air from said air passage through the coal, and meansincluding a damper positioned in the ow path of said air and adapted tobe moved toward and away from its closed position to vary the flow ofair through the coal.

10. A coal burning apparatus including means defining a heat transferchamber, means deiining a separate combustion chamber in the form of abowl having an upwardly and outwardly inclined axis and defining also anupwardly and inwardly inclined passage leading from said bowl into saidheat transfer chamber, a retort supported to extend, at its lower end,into said combustion chamber and adapted to receive coal and deliver itinto the combustion chamber, means defining an air passage extendingentirely around the lower end of said retort for supplying air to thecombustion space throughout the entire circumference of the coalreceiving opening of the combustion chamber, and grate elements arrangedin close relation toeach other along a lower surface of said bowl toprovide tuyre passages leading from said air passage into the lowerportion of the combustion chamber.

DANIEL E. STAIR.

REFERENCES UNITED STA'TEB PATENTS '.Number Number Name Date Maxwell Nov.l, 1921 Sargent Jan. 9, 1923 Burg Feb. 22, 1927' lSchutz Jan. 31, 1928Gainey et al. June 12, 1934 Hoffman Aug. 14, 1934 Kraeft July 2, 1935Kraeft Apr. 20, 1937 Fulton Aug. 9, 1938 Lockwood 4 May 3 0, 1939Raddatz June 20, 1939 Peitz Feb. 20, 1940 Casey Jan. 14, 1941 Fellows'et al Sept. 15, 1942 Fulton -..1..-- Feb. 26, 1946 Sanford et al. July9, 1946 FOREIGN PATENTS Countryv Date Germany May 2, 1923 Great Britain1890 Great Britain Sept. 14, 1925 Netherlands sept. 7, 1933

